<i>In Situ</i> Measurement of Electrical Resistivity of Ocean Sediments Containing Gas Hydrates

Abstract

An understanding of the physical properties of hydrate-bearing sediment is necessary for interpretation of geophysical data collected in field settings. We have conducted a laboratory experiment to measure the electrical property of initially water saturated sediment containing natural gas hydrate. When gas hydrate was formed from pore fluid in ocean sediment, bulk sediment resistivity was significantly increased. The resistivity of the sediment was largely changed below 20% hydrate saturation. With the increasing hydrate saturation, the resistivity of sediment was increased and the resistivity of pore fluid was decrease. In the final process of hydrate formation, the resistivity depression was found mainly due to the transition of gas hydrate morphology. The electrical resistivity of hydrate specimens varied from 1.930 Ohm.m to 3.950 Ohm.m for saturation ranging from 0% to 52.68%. Besides, the dependence of the resistivity index versus hydrate saturation is inconsistent with Archies law. The results of our studies have important implications for quantitative laboratory and field calibration of geophysical measurements within gas hydratebearing intervals.